Height adjustment mechanisms for chair backrests are well known in the art. Typical of the type of mechanism is that disclosed by Donovan in U.S. Pat. No. 4,639,039 granted Jan. 27, 1987. Donovan's mechanism provides for manually positioning and releasably locking a chair backrest in a desired vertical position relative to the chair seat. Donovan uses a channel having a plurality of vertically arranged notches with a cooperating spring biased latch bar and cam surface.
Another exemplary embodiment of a backrest adjustment mechanism is shown by Tornero in U.S. Pat. No. 4,749,230 granted Jun. 7, 1988. Tornero's height adjusting device comprises two guided and slideably interlocking plates and one lock pin. The device is characterized by the absence of springs or other supplementary biasing means.
Applicant believes that an adjustment mechanism which can be of molded plastic, easily produced and yet effective to permit a range of assembly techniques is warranted. An adjustment mechanism which may permit a customer to assemble the chair back to the J-bar of the chair would be advantageous. Alternatively, the manufacturer may assemble the whole structure or the manufacturer may assemble the mechanism together, assemble the mechanism to the J-bar of the chair and subsequently attach the chair back to the mechanism.
The desire to have a relatively inexpensive, yet sturdy adjustment mechanism which permits flexibility in assembly of the chairs, is significant.